Advanced Higher Physics Inductors & Inductance

Magnetic Flux Magnetic flux, , is a measure of the magnetism in an area, given by –  = B A where -  -magnetic flux (Wb) B - magnetic induction (T) A – area perpendicular to magnetic field lines (m 2 )

Solenoids 1 A coil carrying an electrical current is known as a solenoid. The current induces a magnetic field in the coil The direction of the field is determined by the direction of the current in the coil.

Induced EMF 1 Any conductor contains ‘free electrons’ When moving within a magnetic field individual electrons in a conductor experience a force, F = B I l sin , causing them to move This results in an induced EMF. Motion is relative – conductor in field or field past conductor.

Induced EMF 2 SCHOLAR DEMO Size of induced EMF relates to – Speed of motion Direction of motion No. of turns on coil EMF is caused by changing magnetic flux

Induced EMF 3 Magnitude of EMF is related to rate of change of magnetic flux (Faraday’s Law) If the magnetic field strength is changing, an EMF is induced in a conductor placed in the field. So an EMF can be induced by changing the strength of a magnetic field without needing to physically move a magnet or a conductor.

Uses of Magnetic Induction 1 Video & audio cassette players, hard drives are magnetic media. Information is recorded onto a magnetic tape or disc, which passes a coil with an iron core (reading head), inducing a current. The current provides the signal required for the system

Uses of Magnetic Induction 2 Electric guitars use steel strings and magnetic pick- ups As the strings vibrate, the magnetic field of the pick- up changes A coil wrapped around the magnet has a current induced, producing a signal The signal is amplified and sent to a loudspeaker

Uses of Magnetic Induction 3 Microphones have a diaphragm connected to a coil which moves within a magnetic field Sound wave cause the diaphragm and coil to vibrate inside the magnetic field, inducing a current. The signal is amplified and sent to a loudspeaker.